This invention generally relates to the field of rotary driven cylindrical scarifiers for use in roadway surface milling. More particularly, the present invention is directed to wear resistant inserts on abrasive cutting elements for such rotary driven cylindrical scarifiers that may be used on equipment for modifying the surface of an existing road, and in particular, to equipment for smoothing areas of existing pavement by removing bumps, upward projections, and other surface irregularities, removing paint stripes, and milling shallow recessed to receive roadway edging and marking tape.
In general, roadway surface milling, planing, mining or reclaiming equipment disclosed in the prior art includes a rotary driven cylindrical comminuting drum which acts to scarify or mine the top portion of the asphaltic road surface in situ. Road planning machines are used to remove bumps and other irregularities on the surface of a road, runway, taxiway, or other stretch of pavement. This planning effect is typically achieved by grinding the paved surface so that the grinding depth may vary slightly, but the surface produced by the grinding unit is more level than the original surface. The road planning machine typically includes a grinding unit that is powered by an engine or motor. A tractor is attached to, or integral with, the grinding unit for propelling the grinding unit against the paved surface in a desired direction.
In some prior art devices of this type, a plurality of cutter bit support members are connected by bolts or by a weld to the curved surface of a drum or to flighting fixed to a drum surface. The plurality of the support members may be arranged end-to-end so as to form a more or less continuous helical pattern. The top surface of the helically arranged support members may be elevated above the curved surface of the drum. The top surfaces of the cutter bit support members may include angled openings into which conventional cutter bits are received. The cutter bits may be a conical cutter with preferably a tungsten carbide tip or the like. The tip may have a variety of shapes.
Examples of a cutter bit holder and drum are disclosed in U.S. Pat. Nos. 4,480,873; 5,052,757; 7,108,212; 7,290,726; and 7,338,134 to Latham where a rotatable drum has a generally cylindrical outer surface, and a plurality of blocks are mounted onto the outer surface of the drum. The blocks may be positioned onto the drum relative to one another such that the blocks define a helical flight extending around the outer surface of the drum, or may be spaced from each other in any desired pattern. Each of the blocks includes a first side wall, a second side wall, and a top surface. The first and second side walls are generally parallel to one another and generally perpendicular to the drum. The top surfaces of the blocks may define an outer periphery of the flight, if so arranged. Each of the blocks includes a slot and at least one pocket formed therein. The slot is generally rectangular and adapted to receive a tool holder. The slot includes first and second slot side walls, a bottom surface and a rear slot wall. The first and second slot side walls are generally parallel to one another and generally perpendicular to the rear slot wall. The rear slot wall may be oriented at an angle relative to the first and second side walls of the block. A generally rectangular shaped tool or tool holder is received within the slot of each block.
Each block also includes at least one pocket on one of the side walls of the slot. The pocket is generally circular and includes a generally cylindrically shaped retainer positioned therein. Each retainer includes a planar tapered surface that is parallel to and engages one side of the rectangular body of the tool or tool holder within the slot of the block to secure the tool holder in the slot. Each block includes a first hole extending from the second side wall to the rear slot wall. The first hole is oriented generally perpendicular to the rear slot wall. A threaded fastener extends through the hole and engages a threaded bore formed within the tool holder to further secure the tool holder within the slot of the block. Each pocket of each block includes a second hole extending from the pocket to the second side wall that may be oriented generally perpendicular to the second side wall. A threaded fastener may extend through the hole and engage a threaded bore formed within the retainer to pull the retainer within the pocket along a longitudinal axis of the second hole such that the planar tapered surface of the retainer pushes the tool holder against the rear slot wall and the side slot wall to keep the tool holder secured within the slot. This arrangement allows for easy quick replacement of the tool holder when the cutting element or tool held by the tool holder becomes worn or damaged.
More recently, it has been suggested that the cutting surfaces of the cutting tools used in the previously described blocks be formed of a diamond composition such as that disclosed in U.S. Pat. No. 8,501,144 to Bertagnolli. The diamond cutting surfaces may comprise diamond, polycrystalline diamond, natural diamond, synthetic diamond, vapor deposited diamond, silicon bonded diamond, cobalt bonded diamond, thermally stable diamond, infiltrated diamond, layered diamond, cubic boron nitride, diamond impregnated matrix, diamond impregnated carbide, metal catalyzed diamond, or combinations thereof. The diamond cutting surfaces thus formed exhibit extremely long life under the very abrasive environments encountered in roadway surface milling, planing, or reclaiming. The abrasive wear is such that the tool held by the tool holder may degrade from contact with the passing drift to such a point as to require replacement of the tool even though the cutting surface is still performing satisfactorily.
Thus, there exists a need in the art for an apparatus having a cutter bit insert for a milling drum, with or without flighting, that is capable of removable attachment to a drum and is resistant to wear, particularly when the cutting element is an extremely long-lasting diamond cutting surface. There is also a need for a cutter bit that may be quickly removed from the drum and replaced so that the down time experience during cutter bit replacement is minimized.